This invention relates to a process for simulating the appearance of a surface of foamed polypropylene sheet material of a few mils in thickness by printing on a substantially white paper substrate an overall coating of a pearlescent ink and overprinting the pearlescent ink with a dilute black ink in a fine mottled pattern.
In recent years the technology for forming foamed plastic sheets and webs of organic polymeric resins has developed to the point where a substantial number of foamed polymers are available in sheets or webs of various thicknesses for use in a wide variety of applications. Among the more popular foamed plastics if foamed polypropylene which is in substantial demand in webs of a few mils in thickness for use as a packaging material because of its high visual impact and great aesthetic appeal. Foamed polypropylene, either as a self-supporting web or laminated to a suitable substrate such as paper, metal foil or an unfoamed plastic film, has seen its greatest use as a packaging material in the cosmetic field, where the eye appeal of the package is considered to be of great significance in promoting the sale of the product. To this end, luxury bath soaps and other cosmetic products have been packaged in foamed polypropylene because of its velvety sheen which visually imparts the aura of high quality to the product packaged therein.
Foamed polypropylene web stock is, however, a relatively expensive packaging material and it would be desirable if a low-priced substitute material were available which would impart to the beholder the same degree of aesthetic appeal.
Furthermore, foamed polypropylene represents a difficult surface on which to print. The sheet lacks desirable dimensional stability, the surface is quite uneven and the polymer is chemically inert. For these reasons foamed polypropylene sheet material is not ideally suited to the development thereon of the high quality printed images which would be desirable in the decorative and informative indicia associated with the packaging of cosmetic items. It would therefore be highly advantageous if a packaging material could be developed which retained the visual appeal of foamed polypropylene and at the same time presented a superior base for acceptance of very high quality printing such as that obtained through the use of 200 lines per inch rotogravure process printing on a coated paper substrate.
It is therefore an object of this invention to provide a process whereby the appearance of a foamed polypropylene surface may be accurately simulated on an inexpensive paper substrate on which may also be produced process printed images of very high quality. Further objects will become apparent from the following specification and claims.
In an effort to achieve the surface appearance of rare or expensive materials such as finely grained woods, fine fabrics or laces, for example, techniques have been developed which involve photographing the original specimen of the material to be simulated and then, through known printing techniques, reproducing the appearance of the original material as a printed image on paper or a similarly inexpensive substrate. In the case of a simulated wood grain material, for example, the printed paper carrying the image of an expensive, finely grained wood may then be laminated to the surface of an inexpensive wood, chipboard or plastic and overcoated with lacquer or varnish to simulate the appearance of the more expensive original wood grain. This art has achieved such a high degree of success that it is often difficult to distinguish between the original piece of wood and the copy thereof which incorporates a printed paper simulation of the original. Attempts have also been made to simulate the appearance of a foamed polypropylene surface, utilizing the proven techniques of photographing the desired original surface, subjecting the photograph to known color separation procedures to obtain screened negatives and then reproducing the image by multi-color process printing, which procedures have been so successful in the simulation of the appearance of fine grained wood, for example. These attempts have been unsuccessful in the case of foamed polypropylene, the printed image failing to resemble the original surface with any reasonable degree of accuracy, so that no successful printed simulation of a foamed polypropylene surface has hitherto been available.